1. Field of the Invention
This invention involves a package for photosensitive strip material, particularly film. These packages ensure the serviceability of the photosensitive material until it is used. They protect the film from inadvertent exposure and humidity.
2. Description of Related Art
A useful form of package is the so-called wound roll, which has the film wound around a core and protected from light by a cover sheet and two end pieces. The so-called daylight package, which permits a film change in daylight, has been successfully introduced into the market. The roll is generally held on two receptor lugs of an operating device. The cover sheet is partially unwound and fed through a lightproof slit. The cover of the receptor housing is then closed. The receptor can be a fixed component of the device or a cassette. A further tug on the cover sheet makes the film emerge from the slit. In most cases, the cover sheet is now separated from the film and discarded. The forwarding mechanism grips the beginning of the film and transports the film into the exposure chamber of the device. The device is ready for operation. Changing the film does not require a darkroom.
A daylight package of roll film is disclosed, for example, in U.S. Pat. No. 4,148,395. It comprises essentially a cover sheet and two disk-shaped end pieces. It has peripheral, flap-shaped sections that are folded over and adhere on the circumferential surface of the cylinder. Inside, the end pieces adhere on the end faces of the core. However, it has been shown that this package is not lightproof under certain conditions. One problem is that the fold-over produces irregular folds with open spaces and resulting exposure of the outer area of the film roll. Frequently, the adhesion area on the end faces of the core is inadequate as a result of slight mechanical stresses. This results in inadvertent exposure of the film inside the roll.
U.S. Pat. No. 4,505,387 discloses similarly a daylight package for film rolls, in which package a cover sheet wider than the film strip has incisions and is partially folded around the end faces. Here, too, the inner area of the end pieces adheres to the end face of the core and can result in unintentional exposure of the film. In addition, the folds increase the axial measurement of the roll, which is often undesirable.
EP 0,350,093 describes a lightproof package for strip film with a packaging sheet enveloping both the outer circumferential surface and the end faces of a film roll. The overhanging edges are tucked into the core and sealed there in a lightproof manner. The latter step makes this package expensive and can damage the thermosensitive photographic material if a heat-sealing tool is used.
In EP 0,414,265, the parts of the cover sheet extending beyond the width of the film are tucked into the core and held by fasteners. The fasteners and the irregular folds in the cover sheet change substantially the outer dimensions of the roll with respect to certain operating devices and film formats.
EP 0,488,738, EP 0,536,608, and U.S. Pat. No. 4,455,076 disclose packages with rigid flanged disks forming the end faces and with the cover sheet forming a lightproof bead enclosing the periphery. These flanged disks are indeed additional protection against mechanical damage, but they increase the axial length of the film roll.
U.S. Pat. No. 4,826,008 discloses a packaging for film rolls comprising a rigid tube and two end caps inserted into the tube and the roll core. The axial length and the outer diameter of the film roll are increased considerably by the packaging.
Increasing the dimensions of the film roll by the packaging is often not acceptable in the use of the film. The axial spacing of the receptor lugs is indeed adjustable so that narrower film formats can be used, but this spacing is always limited for the largest film formats. The axial length of the film roll frequently exceeds slightly the available inner diameter of the housing. Thus, the film cannot be used in this device because of the packaging. The tolerances for the package measurements can be very narrow. In many instances, a film roll from one manufacturer can fit into an operating device once, but, possibly at another time, cannot be loaded into the same type of apparatus. The standard tolerance ranges for the film manufacturer and the manufacturer of the operating device are indeed observed, but do overlap. Frequently, only fractions of a millimeter decide the serviceability of the film roll.
The film manufacturer strives to size the film roll so that it fits the greatest number of operating units from different companies. In other words, the film manufacturer must adapt its film to the receptor device provided by the unit's manufacturer. This means that the packaging must be shaped so that the dimensions of the film roll, particularly its axial length and the inner diameter of the core, hardly vary. Furthermore, the individual components of a film roll should be as standardized as possible, so that they can be easily processed automatically by packaging machines. Furthermore, after the film is used, the packaging should be easily separable into its different materials for recycling.